People who have beautiful teeth tend to have a favorable impression on others. Demand for aesthetics with respect to teeth has therefore being increasing year by year. In medical treatment and cosmetic treatment in dentistry, when providing a patient's teeth with a prosthetic such as a denture or a crown restoration, the color of the prosthetic is preferably the same color as the adjacently located teeth. It is therefore required in the manufacturing of the prosthetic to precisely discriminate the color of a patient's tooth and manufacture the prosthetic based on the discriminated color. Note that discriminating the color of a tooth in this way is sometimes called tooth-color evaluation (shade taking).
Conventionally, shade guides have been used as color samples for discriminating the color of teeth. A shade guide has a plurality of shade tabs that are a plurality of colors and are arranged according to the colors. Each shade tab is, for example, formed from plastic and shaped as a tooth. Also, each shade tab has been assigned a number for specifying the color of the shade tab.
For example, an observer brings at least one of the shade tabs close to the patient's tooth, and compares the color of the patient's tooth and the color of the shade tab. As a result of the comparison, the observer selects the shade tab whose color is felt to be the closest to the patient's tooth, and discriminates the color of such shade tab as the color of the patient's tooth. Thereafter, for example, the observer notifies a prosthetics manufacturer of the number that specifies the color of the selected shade tab. The prosthetics manufacturer manufactures a prosthesis using materials that give off the same color as the color specified by the number.
In this way, the discrimination of the color of a tooth includes a subjective evaluation by an observer. Subjective evaluations by observers are different from individual to individual, and vary according to the environment at the time of observation. The reliability of the tooth color discrimination result is prone to being low. There is desire for a shade guide that, in order to improve the reliability of the discrimination result, enables a precise discrimination of the color of a tooth by an observer.
The range of colors of shade tabs in conventional shade guides has not covered the range of colors observed for natural teeth. For this reason, there have been cases in which a color close to the color of a tooth targeted for evaluation cannot be found in the shade guide. In order to address this problem, there has been a proposal for a shade guide in which shade tabs whose colors correspond to the distribution range of the colors of natural teeth specified in a color space are arranged (e.g., see Japanese Patent No. 3100809).
However, the above-described conventional shade guide does not take into account visual sensitivity in the actual perception of colors by humans. This shade guide is therefore insufficient for precisely and easily visually discriminating the color of a tooth targeted for evaluation.